This invention relates generally to a process for monitoring the results of a process, and more specifically to a process for planarizing the surface of a work piece and to quantifying the results of a planarization process.
The manufacture of many types of work pieces requires the substantial planarization of at least one surface of the work piece. Examples of such work pieces that require a planar surface include semiconductor wafers, optical blanks, memory disks, and the like. One commonly used technique for planarizing the surface of a work piece is the chemical mechanical planarization (CMP) process. In the CMP process a work piece, held by a work piece carrier head, is pressed against a moving polishing pad in the presence of a polishing slurry. The mechanical abrasion of the surface combined with the chemical interaction of the slurry with the material on the work piece surface ideally produces a planar surface.
The construction of the carrier head, the relative motion between the polishing pad and the carrier head, the composition of the slurry, the composition and texture of the polishing pad, the pressure between the polishing pad and the carrier head, and other process variables have been extensively engineered in an attempt to achieve a uniform removal of material across the surface of the work piece and hence to achieve the desired planar surface. Unfortunately, there has not been an effective technique for the evaluation of the effect of process changes on the uniformity and planarity of the work piece surface. Existing evaluation techniques are inadequate for in depth process evaluation and optimization as they fail to separately quantify the influence of various process parameters. For example, in the semiconductor industry CMP is widely used to planarize the surface of a semiconductor wafer, and a diameter wafer scan of the wafer surface is the most widely used source of information about uniformity and planarity of the wafer surface after the CMP process. Multiple process variables influence the uniformity and planarity, and the diameter wafer scan is not able to adequately distinguish between the affects of those variables. In a diameter wafer scan the amount of material removed from the wafer surface is measured at a plurality of locations along a diameter of the wafer. The measured material removal data is plotted as a function of location along the diameter and the resulting graphical representation can be viewed to obtain a qualitative appraisal of the result of the CMP process. The industrial standard of evaluationxe2x80x94within Wafer Nonuniformity (WIWNU)xe2x80x94evaluates the quality of the wafer surface only from a statistical point of view by calculating the standard deviation of the data. Viewing the results in this manner may provide enough information to form a rough qualitative opinion of process quality, but it provides insufficient information for evaluating process changes and for optimizing and improving the CMP process.
Presently available techniques provide insufficient information for the evaluation and optimization of a planarization process and specifically a CMP process. Accordingly, a need exists for a process for quantifying the results of a CMP process, a planarization process, and indeed, more generally, any process. A need also exists for an improved process for planarizing a surface of a work piece.